The invention relates to a radio system for communication transmission between transmitting-receiving stations moving along prescribed paths and transmitting-receiving stations effective in both the path directions, arranged at prescribed distances alongside of these paths, in which the stations of a path are in communication with a central transmitting-receiving station.
Radio systems of this type have particular importance in railroad systems. The economical utilization of existing rail networks and the high density of the train sequence at the high velocities desired in this context make an increasing data and signal exchange between the trains and the stationary dispatch facilities necessary.
From the publication "Electric Rails" 44 (1973) Vol. 4, pages 83-92 it is known to carry out the information exchange with the aid of a so-called track conductor system. In a track conductor system inductive wire coils are laid out in the track area which are effective as transmitting-receiving antennae for the stationary facilities. The transmission of information between the mobile transmitting-receiving stations on the trains and these stationary facilities proceeds with the aid of frequency keying in the frequency range of about 50 kHz, whereby the maximal transmission rate is limited to about 1200 baud. Aside from this limitation on the rate of the information flow, the track conductor system has the great disadvantage that the wire coils are exposed to the danger of mechanical damage to a large extent, particularly with track superstructure operations.
The danger of mechanical damage can be prevented in such a radio system in that one avoids the transmission with the aid of inductive coils and that the stations in contact with one another exchange their information via radio. Such systems are known, for example, through U.S. Pat. No. 3,517,315. The frequencies utilized therefor lie in the range below one gigahertz (1 GHz). The confinement of radio emission so as to be suited for communication transmission systems operating over substantial distances can only be insufficiently realized in this frequency range. As consequence therefrom results an increased danger of reciprocal interference among the radio services operating in this frequence range. Moreover, the shortage of frequencies available in this range again and again causes considerable difficulties in the construction of networks. The difficulty in the confining of the radio emission of the stations in contact with one another results furthermore in many reflections (because of mountains, buildings, trees, etc.) stemming from outside of the connection direction prescribed. The superpositions of the direct and the reflected emission lead to level breakdowns (response drop-offs) at the receiving station; said level breakdowns are sometimes very deep and may extend at least partially along the path. This phenomenon has to be sometimes taken into consideration in the mobile stations by means of a very expensive receiver technique (diversity technique).